libtls: abort handshake on no ALPN protcol overlap

RFC 7301, section 3.2: In the event that the server supports no
protocols that the client advertises, then the server SHALL respond
with a fatal "no_application_protocol" alert.

This change makes tlsext_alpn_server_process() send the alert
rather than pretending no callback was present.

ok jsing

1 files changed, 2 insertions, 2 deletions

diff --git a/src/lib/libtls/tls_server.c b/src/lib/libtls/tls_server.c
index a94b4221ed..42a697327a 100644
--- a/src/lib/libtls/tls_server.c
+++ b/src/lib/libtls/tls_server.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls_server.c,v 1.51 2024/03/26 08:54:48 joshua Exp $ */
+/* $OpenBSD: tls_server.c,v 1.52 2025/06/04 10:25:30 tb Exp $ */
 /*
  * Copyright (c) 2014 Joel Sing <jsing@openbsd.org>
  *
@@ -75,7 +75,7 @@ tls_server_alpn_cb(SSL *ssl, const unsigned char **out, unsigned char *outlen,
             OPENSSL_NPN_NEGOTIATED)
                 return (SSL_TLSEXT_ERR_OK);
 
-        return (SSL_TLSEXT_ERR_NOACK);
+        return (SSL_TLSEXT_ERR_ALERT_FATAL);
 }
 
 static int